In wireless telecommunication networks, the Long-Term Evolution, or “LTE,” is defined as a standard for wireless communication of high-speed data for mobile phones and data terminals. The LTE standard is developed by the Third Generation Partnership Project (“3GPP”) and the Institute of Electrical and Electronics Engineers (“IEEE”). An exemplary LTE access network is a wireless network of base stations, or evolved NodeBs (“eNBs”), that are interconnected without a centralized intelligent controller. By distributing the intelligence among the eNBs in the LTE network, the time for setting up a connection with a mobile device (e.g., user equipment (“UE”)) is reduced as well as the time required for a handover to another eNB. Furthermore, through the development of the LTE standard, mobile devices are able to increase their capacity and speed using a different radio interface together with core network improvements.
As with any Radio Access Technology, an exemplary LTE network may utilize duplex communications, wherein point-to-point transmissions are composed of two connected devices that communicate with one another in both directions. Thus, a duplex system includes two distinct paths, each carrying information in only one direction. Furthermore, the exemplary LTE network may also utilize channel access methods in point-to-multipoint transmission, wherein forward and reverse communication channels are divided on the same physical communications medium, such as through time-division duplexing (“TDD”) and frequency-division duplexing (“FDD”).
Through the use of TDD and FDD modes, the exemplary LTE system may share the critical resources of time and frequency among mobile subscribers or terminals in the network. FDD uses the idea that the transmission and reception of signals are achieved simultaneously using two different frequencies. Using FDD it is possible to transmit and receive signals simultaneously as the UE is not tuned to the same frequency. TDD may use only a single frequency while sharing the channel between transmission and reception and spacing them apart by multiplexing the two signals on a time basis. TDD mode then shares that single frequency by assigning alternating time slots to transmit and receive operations. Accordingly, TDD is used with data transmissions of a short burst of data in each direction. As the transmission periods are relatively short, no time delay would be noticed on voice transmissions resulting from the time delays introduced by using TDD mode.
With each of the modes, there can be associated disadvantages. For instance, the FDD mode can require a large amount of frequency spectrum, generally at least twice the spectrum needed the TDD mode. In addition, there should be adequate spectrum separation between the transmit/receive channels. Furthermore, with FDD, it can be difficult to utilize special antenna techniques like multiple-input multiple-output (“MIMO”) and beamforming, wherein these technologies are a core part of the LTE network strategies for increasing data rates. Specifically, it can be difficult to make antenna bandwidths broad enough to cover both sets of spectrum.
The primary advantage of TDD mode can be that, unlike FDD mode, the TDD mode only needs a single channel of frequency spectrum. Furthermore, the TDD mode does not require the use spectrum-inefficient guard bands or channel separations as needed in the FDD mode. However, the downside of TDD mode can be that successful implementation may require a very precise timing and synchronization system at both the transmitter and receiver to ensure that time slots do not overlap or otherwise interfere with one another.